CONFIRM: Magnetic Resonance Guided Radiation Therapy

This is a master clinical protocol evaluating magnetic resonance (MR) image guided radiation in patients with gastric and breast cancer. In this research study, the investigators are researching if getting an MRI during radiation is a feasible way to delivery radiation. In this research study, a MRI done during treatment will help doctors adapt the radiation to target the most precise spot where the cancer is located. The research study procedures include: * Screening for eligibility * Study treatment including evaluations * Follow up visits * Questionnaires This is a Phase I/II clinical trial. A Phase I clinical trial tests the safety of investigational radiation treatment and also tries to define the appropriate dose of the investigational radiation treatment to use for further studies. "Investigational" means that the way the radiation treatment is delivered is being studied. This research study is a Feasibility Study, which means it is the first-time investigators at this institution are examining this type of MR-guided radiation. Investigators at other hospitals and academic centers are already using this type of radiation. The U.S. Food and Drug Administration (FDA) has approved this radiation machine and these drugs as treatment options for gastric and breast cancer.